Microwave-assisted synthesis, structural characterization and assessment of the antibacterial activity of some new aminopyridine, pyrrolidine, piperidine and morpholine acetamides

Article abstract of DOI:10.3390/molecules26030533

A series of new acetamide derivatives 22–28 of primary and secondary amines and para-toluene sulphinate sodium salt have been synthesized under microwave irradiation and assessed in vitro for their antibacterial activity against one Gram-positive and two Gram-negative bacterial species such as S. pyogenes, E. coli, and P. mirabilis using the Mueller-Hinton Agar diffusion (well diffusion) method. The synthesized compounds with significant differences in inhibition diameters and MICs were compared with those of amoxicillin, ampicillin, cephalothin, azithromycin and doxycycline. All of the evaluated acetamide derivatives were used with varying inhibition concentrations of 6.25, 12.5, 37.5, 62.5, 87.5, 112.5 and 125 μg/mL. The results show that the most important antibacterial properties were displayed by the synthetic compounds 22 and 24, both of bear a para-chlorophenyl moiety incorporated into the 2-position moiety of acetamide 1. The molecular structures of the new compounds were determined using the FT-IR and¹H-NMR techniques.

Full text of DOI:10.3390/molecules26030533

molecules
Article
Microwave-Assisted Synthesis, Structural Characterization and
Assessment of the Antibacterial Activity of Some New
Aminopyridine, Pyrrolidine, Piperidine and Morpholine
Acetamides
Abdulmajeed S. H. Alsamarrai * and Saba S. Abdulghani
Department of Chemistry, College of Applied Sciences, University of Samarra, Salahaldin 13/1333, Iraq;
sabasabdulghani@gmail.com
* Correspondence: abdulmajeedsalihhamad@yahoo.com or abdulmajeed.s@uosamarra.edu.iq;
Tel.: +964-7707805130
Abstract: A series of new acetamide derivatives 22–28 of primary and secondary amines and para-
toluene sulphinate sodium salt have been synthesized under microwave irradiation and assessed
in vitro for their antibacterial activity against one Gram-positive and two Gram-negative bacterial
species such as S. pyogenes, E. coli, and P. mirabilis using the Mueller-Hinton Agar diffusion (well dif-
fusion) method. The synthesized compounds with significant differences in inhibition diameters and
MICs were compared with those of amoxicillin, ampicillin, cephalothin, azithromycin and doxycy-
cline. All of the evaluated acetamide derivatives were used with varying inhibition concentrations of
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
6.25, 12.5, 37.5, 62.5, 87.5, 112.5 and 125
µg/mL. The results show that the most important antibacterial
properties were displayed by the synthetic compounds 22 and 24, both of bear a para-chlorophenyl
moiety incorporated into the 2-position moiety of acetamide 1. The molecular structures of the new
compounds were determined using the FT-IR and 1H-NMR techniques.
Citation: Alsamarrai, A.S.H.;
Abdulghani, S.S. Microwave-Assisted
Synthesis, Structural Characterization
and Assessment of the Antibacterial
Activity of Some New
Keywords: acetamide; pyridine; pyrrolidine; piperidine; morpholine; antibacterial activity; heterocycles
Aminopyridine, Pyrrolidine,
Piperidine and Morpholine
Acetamides. Molecules 2021, 26, 533.
https://doi.org/10.3390/molecules
26030533
1. Introduction
Several acetamide derivatives have been reported to act as antimicrobial agents
which have been shown to be highly effective against Gram-positive and Gram-negative
Academic Editor:
species [
blocks for the synthesis of complex heterocyclic compounds. Further possible biological
effects have also been shown by derivatives of the acetamide moiety (Figure 1), notably as
antimalarial [ ], anticancer [ ], anti-diabetic [ ], anti-tuberculosis [ ] and anti-inflammatory
1–5]. There are many reports on the use of α-chloroacetamides as useful building
Diego Muñoz-Torrero
Received: 28 September 2020
Accepted: 11 November 2020
Published: 20 January 2021
1
6
7
8
9
agents [10], as well as in industrial applications such as stabilizer synthesis [11], plastic
releasing agents [12], film [13], surfactants and soldering flux [14], organic fibers [15] and
dyes [16].
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional clai-
ms in published maps and institutio-
nal affiliations.
The compounds atorvastatin (
cillin ( ) [20], levobupivacaine ( ) [21] are the most widely used drugs in medicine that
contain the acetamide moiety (Figure 1). Pyrrolidine, piperidine, morpholine, and piper-
2) [17], lidocaine (3) [18], paracetamol (4) [19], amoxi-
5
6
1
azine are secondary amines that are very valuable saturated heterocyclic compounds
because of their wide and diverse range of promising biological activities, such as antibac-
Copyright: © 2021 by the authors. Li-
censee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and con-
ditions of the Creative Commons At-
tribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
terial and anti-inflammatory activity [22
secondary cyclic amines linked to the 1 or 2-positions were reported to be anticonvul-
sant agents. For instance, anticonvulsant compounds such as and are used to treat
and 10 is used to inhibit kinase
–26]. In addition, many derivatives of 1 containing
7
8
epilepsy [27], while the combination of compounds
enzyme and antihistamines [28].
9
Molecules 2021, 26, 533. https://doi.org/10.3390/molecules26030533
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 533
2 of 16
Figure 1. The most widely used drugs in medicine.
Pyridine heterocycles are present in certain biologically active molecules (Figure 2).
One of the pyridine-containing medications is Lunesta with the active ingredient 11 that is
used to treat insomnia, and pioglitazone 12 which is effective in diabetes care.
O
O
N
N
N
O
N
Cl
HN
S
O
N
O
O
N
pioglitazone
12
N
S-zoplicone 11
O
O
NH
O
S
OCF3
F
N
N
O
N
N
NH2
N
antifungal agent
antituberculosis agent
13
14
Figure 2. Some biologically active molecules containing pyridines.

Molecules 2021, 26, 533
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In addition, previous studies conducted by Nakamoto et al. [29] and Tang et al. [30
]
evaluated the compounds 13 and 14 as an antifungal and antituberculous agent,
respectively.
The synthesis of compounds with broad antibacterial activity is required because of
the extensive use of antibiotics in medicine and the prevailing resistance of microorganisms.
Conventional organic preparation methods are too sluggish to meet the need for the
rapid synthesis of these compounds. Nowadays microwave irradiation represents an
interesting technique to be applied in organic synthesis [31]. Herein, we report the use
of microwaves in the synthesis of seven new acetamide derivatives 22–28 by reaction
of chloroacetyl chloride 15 with primary, secondary amines and para-toluene sulphinate
sodium salts. In addition, the aim of this study was to assess the susceptibility profile of
bacterial isolates to the synthesized compounds 22
determine their minimum inhibition concentrations (MICs). The structures of compounds
22
28 were determined by 1H-NMR, and FT-IR and elemental analysis. Table 1 shows the
approach followed.
–28 and reference antibiotics, and to
–
Table 1. Melting points, colours, solvents for recrystallization, and yields of the compounds 16–28.
M. P.
C
Yield% of
Conventional Method
Yield% of
Microwave Method
Comp. No.
Recryst. Solvent
Color
◦
16
17
18
n-Hexane
Ethanol
Ethanol
Gray
White
Brown
143–145
202–203
276–278
78
85
60
n-Hexane:methanol
19
20
Brown
White
196–198
251–253
83
80
1:3
Ethyl acetate:acetone
1:1
21
22
23
n-Hexane
n-Hexane
Ethanol
Brown
Gray
198–200
183–185
188–189
90
24
55
50
85
Yellow
n-Hexane:ethanol
24
White
197–198
55
78
1:3
Ethyl acetate:ethanol
1:1
25
26
27
28
White
white
White
Brown
170–172
204–207
251–253
212–213
30
53
60
50
90
78
76
62
Methanol
n-Hexane:methanol
1:1
Ethanol
2. Results and Discussion
2.1. Chemistry
We are engaged in intensive efforts to synthesize nitrogen-heterocyclic compounds
in high yields. Following a previously described study [32], the -chloroacetamide inter-
mediates 16 21 and the new targeted derivatives 22 28 were designed and synthesized by
α
–
–
introducing para-toluene sulphinate, pyrrolidinyl, morpholinyl, and piperidinyl moieties
into the acetamide scaffold as can be seen in Scheme 1.
Over the past thirty years, microwave irradiation has been used to enhance reaction
rates [33
,34]. We have thus exploited the advance of microwave technology to accelerate
the creation of C-N bonds. For the synthesis of the precursors 16
–
21, the process was
performed under mild conditions involving the addition of chloroacetyl chloride 15 to a
mixture of amines and para-toluene sulphinate sodium salt in dry CH2Cl2 at 0 ◦C and the

Molecules 2021, 26, 533
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isolated yields of these compounds ranged from 60 to 90% (see Table 1). The synthesis of
targeted compounds 22
microwave irradiation. The heating process involved precursors 16
–
28 was achieved through two routes: conventional heating and
21, amine, and sodium
–
para-toluene sulphinate reactions in a CH3CN solution containing Et3N as a catalyst giving
◦
the compounds 22
–
28 in moderate yields reaching 60% at 70 C (see Scheme 1 and Table 1),
On the other hand, treatment of the precursors 16
para-toluene sulphinate in dry CH3CN provided the desired compounds 22
–
21 with amines as well as sodium
◦
–
28 at 65–70 C
in good yields under microwave irradiation. The reactions took 5–10 min to complete and
one of the advantages of this technique is allowed us to isolate clean products in good
yields and without side products (see Tables 1 and 2 for the corresponding 1H-NMR data).
Scheme 1. Synthetic pathway to compounds 22–28.
2.2. In Vitro Antibacterial Activity Testing
Instructive bacterial infections such as tuberculosis, urinary tract infection, pneumonia,
brain abscess, phyaryngitis, and tonsillitis are a series of life-threatening diseases commonly
recognized in immunocompromised patients. Such infectious diseases are becoming more
and more resistant to antibiotics. Resistance to microbial drugs is an inevitable consequence
of the overuse of antibacterial drugs. Susceptibility to antibiotics by pathogens has now
become a crucial factor in the effectiveness of chosen antibacterial drugs. Amoxicillin,
ampicillin, doxycycline, azithromycin and cephalothin, the five reference antibiotics used
in this research, are commonly used for the treatment of infections. Researchers continue
to seek new antimicrobial agents. This research was carried out to determine the suscep-
tibility of certain bacterial organisms toward seven newly synthesized compounds. The

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synthesized compounds 22
–28 have been evaluated for antibacterial activity in comparison
with the abovementioned reference antibiotics.
1
Table 2. H-NMR data of compounds 22–28.
Chemical Shift
Structure
Signal Features
No. of Protons
Type of Protons
(δ) ppm
dd, J2,3 5.25 Hz, J2,6 1.30
7.20–6.75
6.32
3.36 and 1.75
3.30
4H
1H
8H
2H
aromatic
NH
pyrrolidinyl proton
-CH2CO-
Hz
s
2m
s
22
dd, J2,3 5.35 Hz, J2,6 1.30
7.75–7.42
4.20
2.85 and 1.90
2.35
4H
2H
8H
3H
tolyl
-CH2CO-
pyrrolidinyl proton
CH3
Hz
s
2m
s
23
24
25
dd, J2,3 5.0 Hz, J2,6 1.45
7.20–6.70
6.35
3.20
2.90 and 1.45
4H
1H
2H
aromatic
NH
-CH2CO-
Hz
s
s
10H
piperidinyl proton
2 m
dd, J2,3 5.26 Hz, J2,6 1.4
7.75–7.42
4.15
3.70 and 2.50
2.40
4H
2H
8H
3H
tolyl protons
-CH2CO
morpholinyl protons
CH3
Hz
s
2t
s
s
s
10.65
9.0
8.41–7.10
7.70–7.35
4.20
1H
1H
3H
4H
2H
3H
NH
pyridinyl proton
pyridinyl protons
tolyl protons
CH2
dd, J4,5 5.31 Hz, J5,6 5.25
Hz
26
dd, J2,3 5.25 Hz, J2,6 1.5
Hz
s
2.35
CH3
s
s
9.90
8.41–7.91
7.65–6.40
4.25
1H
4H
4H
2H
3H
NH
pyridinyl protons
tolyl protons
CH2
dd, J2,3 5,31 Hz., J2,6
1.45 Hz
dd, J2,3 5.20, J2,6 1.5 Hz
27
28
s
s
2.32
CH3
s
2s
10.40
8.30–7.40
7.60–7.45
4.25
1H
2H
4H
2H
9H
NH
pyridinyl proton
tolyl protons
CH2
dd, J2,3 5.26 Hz, J2,6 1.55
Hz
s
3s
2.45–2.35
3CH3
Acetamide derivatives are well known to have a broad range of antibacterial ac-
tions [35]. With regards to our recent research [32] on the synthesis of acetamide deriva-
tives and the assessment of their biological role, in this in vitro study, three species of
microorganisms were included, and all isolates of the three species were susceptible to the
synthesized compounds 22–28 at MICs greater than 6.25 µg/mL.
Tested compounds 22 and 23, exhibited inhibition zones ranging from 6.0 to 8.4 mm
at MIC of 12.5
urinary tract infections (UTI) in patients, while isolates of these bacterial species were
not susceptible to compounds 26 and 28 even at an MIC of 37.5 g/mL. Compounds 24
µg/mL against the Gram-negative species E. coli and P. mirabilis that cause
µ
,

Molecules 2021, 26, 533
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25, and 27 showed inhibition zones ranging from 6 to 14 mm at a MIC of 37.5
µg/mL
(
Figures 3 and 4, and Table S1). These intermediate results are in agreement with other
authors who have reported inhibition zones ranging from between 11 to 12 mm using
amoxicillin (20 µg) and ampicillin (20 µg) [36–38] antimicrobial disks (Tables S1 and S2).
The Gram-positive species S. pyogenes are one of the main causes of urinary tract infec-
tions and poses a significant health concern causing a number of human diseases [39,40]
.
S. pyogenes is also considered to be the most common and significant cause of bacterial
tonsillitis in children and adults. Isolates of this bacterial species obtained from the Tikrit
Teaching Hospital (Tikrit, Iraq) were all susceptible to the synthesized compounds 22
MICs of 12.5 g/mL, and compounds 27 and 28 did not display any inhibition zones in
this test, even at a MIC of 37.5 µg/mL (see Figure 5 and Table S3).
For the sake of comparison, we compared the antibacterial susceptibility of all the
isolates to the five antibacterial agents amoxicillin (20 g), ampicillin (25 g), cephalothin
(30 g), azithromycin (15 g) and doxycycline (30 g) by the disc diffusion process. Isolates
–28 at
µ
µ
µ
µ
µ
µ
of the three species were susceptible to the five antibiotics and displayed inhibition zones
ranging from 5.8–19 mm. S. pyogenes isolates showed intermediate zones ranging from
5.8–7.6 mm compared to other Gram-negative species isolates (see Figure 5, Table S3).
All species included in this research, however, were more susceptible to the synthe-
sized compounds 22–28 at higher MICs ranging from 37.5 to 125 µg/mL compared to the
control antibiotics. This low activity may, potentially, be caused by resistance-acquiring
bacteria due to the arbitrary use of antibiotics by patients [41–43].
The aim of this study was also to observe any relation between the structure of the
synthesized compounds 22
them. Thus, as described earlier, the antibacterial susceptibility of compounds 22
antibiotics given as MIC values in g/mL were used to achieve this goal. For compounds
22 28, Figures 3–5 clearly indicate that E. coli is more susceptible to compounds 22 23
and 12, while P. mirabilis is more susceptible to compounds 22 and 24 as is S. pyogenes (see
Figure 5). The presence of a para-chlorophenyl moiety at the 2-position of the unit of
–
28 and the susceptibility of the bacterial isolates towards
–
28 and
µ
–
,
,
1
these compounds appears to be responsible for this effect. The presence of a chlorine atom
presumably makes such compounds more active than other compounds against the isolates
of the three bacterial species. In case of antibiotics, E. coli tends to be more susceptible to
these five antibiotics, and there were few variations among the isolates’ responses to the
antibiotics (see Figures 3–5).
As previously mentioned, several pyridine compounds have been shown to possess
antibacterial activity [29
in an attempt to enhance the antibacterial activity of the targeted compounds 22
,
30]. In the present study, it appears that the use of aminopyridines
28 is
–
not encouraging. Recently, there is a growing interest in the use of drugs of choice as
quaternary pyridinium salts to improve their solubility and thus to boost the antibacterial
activity due to the presence of quaternary ammonium salts [44].
In order to equate the susceptibility of the more active synthesized compounds, which
in this case were compounds 22 and 24 with antibiotics against the bacterial species used
in the study, the antibiotics exhibited susceptibility against E. coli two-fold greater than
compounds 22 and 24, while antibiotics exhibited susceptibility against S. pyogenes two-fold
lower than compounds 22 and 24. Antibiotics demonstrated the same activity against P.
mirabilis as compounds 22 and 24. The comparison was made using a concentration of
37.5
µg/mL for compounds 22 and 24 close to the contents of antibiotic discs (see Table 3,
Figure 6).

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Figure 3. Antibacterial susceptibility of species E. coli given as MICs values in µg/mL for compounds 22–28.

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Figure 4. Antibacterial susceptibility of species P. mirabilis given as MICs values in µg/mL for compounds 22–28.

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Figure 5. Antibacterial susceptibility of species S. pyogenes given as MICs values in µg/mL for compounds 22–28.

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Table 3. Inhibition zone diameters (mm) of reference antibiotics and synthesized compounds 22
and 24.
Amx
Azi
Doxy
Cep
Am
22
24
20 µg
15 µg
30 µg
30 µg
25 µg
37.5 µg/mL
37.5 µg/mL
E. coli
P. mirabilis
S. pyogenes
12.3
12.8
5.8
17.0
11.0
6.5
19.0
13.0
7.3
13.5
11.0
7.6
16.0
7.5
6.4
7.7
14.2
15.0
5.8
12.9
13.0
Figure 6. Antibacterial susceptibility of some species bacteria given as MICs values in µg/mL for referenced antibiotics.
3. Materials and Methods
3.1. General Information
Melting points were measured using an open capillary on a Buchi melting point
apparatus Buchi labortechnik AG, Essen, Germany, and are uncorrected. All the required
chemicals used were purchased from Aldrich (Hamburg, Germany). Thin layer chromatog-
raphy (TLC) was carried out on 5
×
5 plates coated with silica 0.25 cm N-HR/UV254
obtained from Merck (Dramstadt, Germany). IR spectra were recorded over a frequency
range of 4000–400 cm−1 on a FT-IR 8400S spectrophotometer (Shimadzu, Tokyo, Japan).
1H-NMR spectra were recorded on a 300 MHz spectrometer (Tehran, Islamic Republic of
Iran) using different solvents and TMS as internal reference Chemical shifts are expressed
relative to the internal standard on the
δ scale in ppm. Elemental analyses (CHN) were
determined on an Eur.Vector EA 3000A system (Rome, Italy). Microwave experiments
were conducted using a Microwave Synthesis WorkStation (MAS-II, Microwave Chemistry
Technology, Shanghai, China)

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3.2. Chemistry
3.2.1. General procedure for the preparation of derivatives 16–21
Following a previous report [32], an equivalent quantity of 2-chloroacetyl chloride
(2 g, 0.0176 mol) was added to a stirred and cooled solution of the appropriate secondary
amine pyrrolidine, morpholine, piperidine, 2,4-dimethylaminopyridine, 2-aminopyridine,
3-aminopyridine and 4-aminopyridine (0.0176 mol) in dry dichloromethane (12 mL), con-
taining equivalent quantities of triethylamine (0.0178 mol) as a base. The reaction mixtures
were then stirred at room temperature for 1–2 h. Reaction progress was tracked via TLC.
Once the reactions were complete, aqueous sodium carbonate was added with shaking
until the medium became neutral. The organic layers were washed with water separately
and dried over anhydrous magnesium sulfate. The solvents were removed under vacuum
and the residual materials treated with ether to give crystalline samples of of 2-chloro
(pyrrolidinyl, morpholinyl, piperazinyl, pyperidinyl, pyridin-2-yl, pyridin-3-yl, pyridin-
4-yl, 4,6-dimethyl pyridine-2-yl) acetamides 16
solvents gave pure derivatives 16–21.
–21, and recrystallization from different
2-Chloro-1-(pyrrolidine-1-yl)ethan-1-one (16). Grey crystals, m.p., 143–145 ◦C; (Yield:
2.8 g, 78%);
υ
[KBr]: 2986 cm−1 (C-H aliphatic); 1635 cm−1 (C=O amide); 1452 cm−1
max
(C-N); 707 cm−1 (C-Cl).
2-Chloro-1-(piperidin-1-yl)ethan-1-one (17). White crystals, m.p., 202–203 ◦C; (Yield:
2.5 g, 85%);
υ
[KBr]: 2945 cm−1 (C-H aliphatic); 1708 cm−1 (C=O amide); 1506 cm−1
max
(C-N); 746 cm−1 (C-Cl).
2-Chloro-1-morpholinoethan-1-one (18). Brown crystals, m.p., 198–200 C; (Yield:
2.7 g, 60%);
[KBr]: 2975 cm−1 (C-H aliphatic); 1650 cm−1 (C=O amide); 1437 cm−1
◦
υ
max
(C-N); 732 cm−1 (C-Cl).
2-Chloro-N-(pyridin-3-yl)acetamide (19). Brown crystals, m.p., 196–198 C; (Yield:
◦
4.1 g, 83%);
υ
[KBr]: 3500 cm−1 (N-H amide); 3040 cm−1 (C-H aromatic); 2981 cm−1
max
(C-H aliphatic); 1654 cm−1 (C=O amide); 1575 cm−1 (C=C); 1477 cm−1 (C-N); 740 cm−1
(C-Cl).
◦
2-Chloro-N-(pyridin-4-yl)acetamide (20). White crystals, m.p., 251–253 C; (Yield:3.9 g,
80%);
υ
[KBr]: 3346 cm−1 (N-H amide); 3051 cm−1 (C-H aromatic); 2941 cm−1 (C-H
max
aliphatic); 1677 cm−1 (C=O amide); 1550 cm−1 (C=C); 1460 cm−1 (C-N); 578 cm−1 (C-Cl).
◦2-Chloro-N-(4,6-dimethylpyridin-2-yl)acetamide (21). Brown cr−y1stals, m.p., 267–
−1
278 C; (Yield: 2.6 g, 90%);
υ
[KBr]: 3307 cm (N-H amide); 3074 cm (C-H aromatic);
max
2947 cm−1 (C-H aliphatic); 1656 cm−1 (C=O amide); 1575 cm−1 (C=C); 1545 cm−1 (C-N);
743 cm−1 (C-Cl).
3.2.2. General Procedure for the Preparation of Derivatives 22–28
(A) Conventional Method
The compounds 22–28 synthesized as previously reported [32] by combining equiva-
lent amounts of the acetamide 16 (0.2 g, 0.0013 mol) with substituted para-chloro aniline
(0.17 g, 0.0013 mol) in dry acetonitrile (7 mL) containing an equivalent amount of triethy-
◦
lamine as a catalyst. The mixture is heated for 2–3 h at 70 C, and the progress of reactions
tracked by TLC until the starting materials disappeared. Upon reaction completion, the
reaction mixture was cooled to room temperature, the solvent was removed under vacuum
and the residue taken up in CH2Cl2 (10 mL), treated with aqueous K2CO3 until neutraliza-
tion, the organic layer washed with water, isolated and dried over anhydrous magnesium
sulphate. The solvent was removed in vacuo, and the resulting gummy materials treated
with ether, resulting in crystalline derivatives of 22 (see Table 1). Compounds 23–28 were
synthesized similarly by using equivalent amounts of starting materials.
((4-Chlorophenyl)amino)-1-(3-rrolidine-1-yl)ethan-1-one (22). Grey crystals, m.p., 183–
185 ◦C; (Yield: 0.17 g, 50%); calculated. C, 60.31; H, 6.28; N, 11.76. C12H15N2OCl Founded.
C, 60.01; H, 6.02; N, 11.45;
υ
[KBr]: 3132 cm−1 (N-H); 3078 cm−1 (C-H aromatic);
max
2989 cm−1 (C-H aliphatic); 1679 cm−1 (C=O amide); 1583 cm−1 (C=C); 1541 cm−1 (C-N);
1
690 cm−1 (C-Cl). H-NMR (DMSO-d6):
δ 7.20–6.75 (4H, dd, J2,3 5.25, J2,6 1.30 Hz, aromatic);

Molecules 2021, 26, 533
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6.32 (1H, s, N-H); 3.36 and 1.60 (8H, 2m, pyrrolidinyl protons); and ppm 3.30 (2H, s,
-CH2CO-).
1-(Pyrrolidin-1-yl)-2-tosylethan-1-one (23). Yellow crystals, m.p., 188–189 ◦C; (Yield:
0.29 g, 85%); calculated. C, 58.42; H, 6.23; N, 5.24. C13H17NO3S Founded. C, 58.10; −H1,
−1 −1
[KBr]: 3068 cm (C-H aromatic); 2931 cm (C-H aliphatic); 1676 cm
max
6.02; N, 5.11;
υ
(C=O amide); 1562 cm−1 (C=C); 1515 cm−1 (C-N); 1321 cm−1; 1153 cm−1; 611 cm−1 (S=O);
1H-NMR (DMSO-d6):
δ
7.75–7.42 (4H, dd, J2,3 5.35, J2,6 1.30 Hz, aromatic, tolyl protons);
3.20 (2H, s, -CH2CO-); 2.90 and 1.45 (8H, 2m, pyrrolidinyl protons), 2.35 ppm (3H, s, CH3).
1-(Piperidin-1-yl)-2-tosylethan-1-one (24). White crystals, m.p., 204–207 ◦C; (Yield:
0.27 g, 78%); calculated. C, 61.17; H, 6.73; N, 11.08. C13H17N2OCl Founded. C, 60.85;
H, 6.90; N, 10.30;
υ
[KBr]: 3298 cm−1 (N-H); 3031 cm−1 (C-H aromatic); 2977 cm−1
max
(C-H aliphatic); 1647 cm−1 (C=O amide); 1515 cm−1 (C=C); 1460 cm−1 (C-N); 1357 cm−1
;
1174 cm−1; 580 cm−1 (S=O); H-NMR (DMSO-d6):
δ 7.20–6.70 (4H, dd, J2,3 5.30, J2,6
1
1.45 Hz, aromatic); 6.35 (1H, s, N-H); 3.20 (2H, s, -CH2CO-); 2.90 and 1.45 ppm (10H, 2m,
piperidinyl protons).
◦
1-Morpholino-2-tosylethan-1-one (25). White crystals, m.p., 170–172 C; (Yield: 0.31 g,
90%); calculated. C, 55.12; H, 6.0; N, 4.94. C13H17NO4S Founded. C, 54.90; H, 6.10; N,
5.08;
amide); 1581 cm−1 (C=C); 1539 cm−1 (C-N); 1247 cm−1; 1172 cm−1; 584 cm−1 (S=O); 1H-
NMR (DMSO-d6): 7.75–7.42 (4H, dd, J2,3 5.25 Hz, J2,6 1.4 Hz, tolyl protons), 4.15 (2H, 2,
υ
max [KBr]: 3099 cm−1 (C-H aromatic); 2974 cm−1 (C-H aliphatic); 1679 cm−1 (C=O
δ
-CH2CO-); 3.70 and 2.50 (8H, mm, morpholinyl protons), 2.40 ppm (3H, s, CH3).
◦
N-(Pyridin-3-yl)-2-tosylacetamide (26). White crystals, m.p., 204–207 C; (Yield: 0.27 g,
78%); calculated. C, 57.93; H, 4.82; N, 9.65. C14H14N2O3S Founded. C, 58.20; H, 5.02; N,
9.50;
υ
[KBr]: 3298 cm−1 (N-H); 3031 cm−1 (C-H aromatic); 2977 cm−1 (C-H aliphatic);
max
1647 cm−1 (C=O amide); 1515 cm−1 (C=C); 1460 cm−1 (C-N); 1357 cm−1; 1174 cm−1
;
580 cm−1 (S=O); 1H-NMR (DMSO-d6):
δ
10.61 ppm (N-H, s); 10.65 (1H, s, N-H); 9.0 (1H,
δ
s, pyridinyl proton); 8.41–7.10 (3H, dd, J4,5 5.31, J5,6 5.25 Hz, J2,6 1.5 Hz, pyridinyl proton);
7.70–7.35 (4H, dd, J2,3 5.25 Hz, tolyl protons); 4.20 (2H, s, -CH2CO-); and 2.35 ppm (3H,
s, CH3).
◦
N-(Pyridin-4-yl)-2-tosylacetamide (27).White crystals, m.p., 251–253 C; (Yield: 0.26 g,
76%); calculated. C, 57.93; H, 4.82; N, 9.65. C14H14N2O3S Founded. C, 57.60; H, 5.0; N,
9.61;
υ
[KBr]: 3344 cm−1 (N-H); 3080 cm−1 (C-H aromatic); 2977 cm−1 (C-H aliphatic);
max
1639 cm−1 (C=O amide); 1531 cm−1 (C=C); 1461 cm−1 (C-N); 1365 cm−1; 1103 cm−1
;
557 cm (S=O); 1H-NMR (DMSO-d6):
J2,6 1.5 Hz, pyridinyl protons);
4.25 (2H, s, -CH2CO-); and 2.32 ppm (3H, s, CH3).
δ
9.90 (1H, s, N-H);
δ
8.41–7.91(4H, dd, J2,3 5.31 Hz,
−1
δ
7.65–6.40 (4H, dd, J2,3 5.20 Hz, J2,6 1.5 Hz, tolyl protons); δ
◦
N-(4,6-Dimethylpyridin-2-yl)-2-tosylacetamide (28). Brown crystals, m.p., 212–213 C;
(Yield: 0.21 g, 62%); calculated. C, 60.37; H, 5.66; N, 8.80. C16H18N2O3S Founded. C, 60.57;
H, 5.42; N, 8.91;
(C-H aliphatic); 1677 cm−1 (C=O amide); 1596 cm−1 (C=C); 1544 cm−1 (C-N); 1336 cm−1
1150 cm−1; 524 cm−1 (S=O); 1H-NMR (DMSO-d6):
10.40 (1H, s, N-H); 8.30–7.40 (2H, 2s,
υ
[KBr]: 3463 cm−1 (N-H); 3085 cm−1 (C-H aromatic) ; 2945 cm−1
max
;
δ
pyridinyl protons); 7.60–7.45 (4H, dd, J2,3 5.25 Hz, J2,6 1.55 Hz, tolyl protons); 4.25 (2H, s,
-CH2CO-); and 2.45–2.35 ppm (9H, s, 3CH3).
(B) Microwave Method
The compounds 22
lent quantities mentioned in the above experiments, substituted aniline and para-toluene
sulfonate sodium salt with -chloroacetamides 16 21 in dry acetonitrile (7 mL) containing
–28 synthesized as previously stated [32] by combining the equiva-
α
–
equivalent quantities of triethylamine as a catalyst. The mixture was heated at 65–70 ◦C
under 400 Watt microwave irradiation for 5–10 min. The reaction progress was monitored
with TLC until the starting materials had disappeared. After the reaction was completed,
the mixture was cooled to room temperature, the solvent removed under vacuum, and the
residue taken in CH2Cl2 (10 mL) and treated with aqueous K2CO3 until neutralization, then
the organic layer was washed with water, separated and dried over anhydrous magnesium

Molecules 2021, 26, 533
13 of 16
sulfate. The solvent was removed under vacuum, and the resulting gummy products 22
–28
treated with ether to give crystalline products 22–28 (See Table 1).
3.3. Antibiotics
Ready-impregnated antibiotic disks of amoxicillin (20 mcg), ampicillin (25 mcg),
cephalothin (30 mcg), azithromycin (15 mcg) and doxycycline (30 mcg) were obtained
from Samarra Drug Industries, (Samarra, Iraq) and were used as standard broad-spectrum
antibacterial agents in the disk diffusion method.
3.4. Bacterial Species
Isolates of the three different bacterial species, namely, two Gram-negative bacteria
(E. coli plus P. mirabilis) and one Gram-positive bacterium (S. pyogenes) were collected from
the Tikrit Teaching Hospital (Tikrit, Iraq). All the isolates of E. coli and P. mirabilis were
collected from urine samples of urinary tract infection (UTI) patients and the isolates of
S. pyogenes were collected from tonsillitis patients.
3.5. Antibacterial Susceptibility Testing
Antibacterial resistance to seven new synthesized compounds 22–28 of the acetamide
class and five antibiotics, including amoxicillin, ampicillin, cephalothin, azithromycin and
doxycycline, was evaluated using the standard disk diffusion method [45] and the diffusion
method (well diffusion) for synthesized compounds 22–28. Both studied bacterial species
were pre-cultivated on 24 h incubated nutrient agar plates and bacterial suspensions of each
pure isolate were prepared for in vitro antibacterial treatment in 0.6 McFarland turbidity
nutrient broth tubes. Mueller Hinton agar plates (Oxoid Ltd., Hampshire, UK), 12 cm in
diameter, were prepared as directed by the manufacturer and incubated at 37 ◦C for 24 h.
So, a sterile borer was used to make equidistant wells with a diameter of 6 mm. 50 mg
of each of the synthetic compounds 22
dilution of 2.5, 5, 15, 25, 35, 45 and 50 L of each to 1 mL DMSO to obtain concentrations
of 0.125, 0.250, 0.750, 1.25, 1.75, 2.25 and 2.5 mg/mL which equivalent to 6.25, 12.5, 37.5,
62.5, 87.5, 112.5 and 125 g/50, respectively. 50 L of each of the later concentrations were
–28 was dissolved in DMSO (1 mL), followed by
µ
µ
µ
used to assess antibacterial susceptibility and minimum inhibitory concentrations (MICs)
by filling the growth media wells with it accompanied by 24-h incubation at 37 ◦C and
growth inhibition monitor in. DMSO did not display any inhibition of bacterial growth.
3.6. Analysis of Results
SPSS software (version 20, IBM, Armonk, NY, USA, www.ibm.com/software/analytics/
spss) was used to evaluate the effects of the antimicrobial susceptibility study. Mean values
and standard deviations for the inhibition zone diameters were determined. The findings
were presented as average values
calculated relative to normal antibiotics and the amount of dispersion between them.
±
SD. Statistically standard deviation, variations are
4. Conclusions
2-Chloroacetamides are versatile intermediates in organic synthesis. The reported
synthesis method is based primarily on chloroacetylation of amines by chloroacetyl chlo-
ride. The simple replacement of a chlorine atom allowed us to prepare many acetamide
derivatives through the reaction with amines and para-tosyl sodium salt. A series of new
acetamide derivatives were successfully synthesized by adding primary and secondary
amines to chloroacetyl chloride 15. With the help of microwave irradiation, we have been
able to synthesize seven compounds in an attempt to increase yields and reduce the reac-
tion time. Moderate to good yields and reduction of the reaction time from 2–3 h to a few
minutes were achieved. The application of the compounds 22–28 against Gram-positive
and Gram-negative bacterial species demonstrated encouraging relatively good antibacte-
rial potency in comparison with the used reference antibiotics. Isolates of two of the tested
species, namely, E. coli and P. mirabilis displaced higher susceptibility than S. pyogenes. The

Molecules 2021, 26, 533
14 of 16
results show that among synthetic compounds 22
–
28 compounds 22 and 24 present the
most important antibacterial properties bearing para-chlorophenyl moiety in the acetamide
2-position of moiety . We have successfully developed a synthetic method has proven
1
to be a fast, environmentally friendly technique with moderate to good performance in
microwave irradiation, and high acceleration of reaction rates has been achieved in the
presence of Et3N as a base.
Supplementary Materials: The following are available online. Table S1, Table S2, and Table S3.
Author Contributions: Conceptualization, A.S.H.A.; methodology, S.S.A., S.S.A.; validation, A.S.H.A.,
S.S.A.; formal analysis A.S.H.A., S.S.A.; investigation, A.S.H.A.; resources, S.S.A.; data curation S.S.A,;
writing—original draft preparation, A.S.H.A.; writing—review and editing A.S.H.A; visualization,
A.S.H.A.; supervision, A.S.H.A.; project administration, A.S.H.A.; funding acquisition, A.S.H.A. All
authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available in article and Supple-
mentary Material.
Acknowledgments: The authors thank the Department of Chemistry, College of Applied Science,
Samarra University, Iraq, for supporting facilities. The authors also thank Maroof S. Juma for technical
assistance and Faesal G. Hussein for helpful comments.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are not available from the authors.
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